Nature
Mole Hill, west of Harrisonburg in Virginia's Shenandoah Valley, is the eroded basalt remnant of an ancient volcano that formed about 47 million years ago during the Eocene. Rising from otherwise flat farmland, it is one of the youngest volcanoes on North America's east coast and part of a broader episode of volcanic activity in Virginia and West Virginia between about 48 and 35 million years ago. Its basalt pierced much older Ordovician carbonate rock, and geologists now link its eruption to crustal extension and decompression melting rather than plate-boundary volcanism. Radiometric dating in 1969 established its much younger age and clarified its significance in Appalachian geology.
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Virginia · United States
